On Tue, 15 Jan 2008, Andrew Morton wrote: > On Tue, 15 Jan 2008 21:01:17 -0800 (PST) dean gaudet <[EMAIL PROTECTED]> > wrote: > > > On Mon, 14 Jan 2008, NeilBrown wrote: > > > > > > > > raid5's 'make_request' function calls generic_make_request on > > > underlying devices and if we run out of stripe heads, it could end up > > > waiting for one of those requests to complete. > > > This is bad as recursive calls to generic_make_request go on a queue > > > and are not even attempted until make_request completes. > > > > > > So: don't make any generic_make_request calls in raid5 make_request > > > until all waiting has been done. We do this by simply setting > > > STRIPE_HANDLE instead of calling handle_stripe(). > > > > > > If we need more stripe_heads, raid5d will get called to process the > > > pending stripe_heads which will call generic_make_request from a > > > different thread where no deadlock will happen. > > > > > > > > > This change by itself causes a performance hit. So add a change so > > > that raid5_activate_delayed is only called at unplug time, never in > > > raid5. This seems to bring back the performance numbers. Calling it > > > in raid5d was sometimes too soon... > > > > > > Cc: "Dan Williams" <[EMAIL PROTECTED]> > > > Signed-off-by: Neil Brown <[EMAIL PROTECTED]> > > > > probably doesn't matter, but for the record: > > > > Tested-by: dean gaudet <[EMAIL PROTECTED]> > > > > this time i tested with internal and external bitmaps and it survived 8h > > and 14h resp. under the parallel tar workload i used to reproduce the > > hang. > > > > btw this should probably be a candidate for 2.6.22 and .23 stable. > > > > hm, Neil said > > The first fixes a bug which could make it a candidate for 24-final. > However it is a deadlock that seems to occur very rarely, and has been in > mainline since 2.6.22. So letting it into one more release shouldn't be > a big problem. While the fix is fairly simple, it could have some > unexpected consequences, so I'd rather go for the next cycle. > > food fight! >
heheh. it's really easy to reproduce the hang without the patch -- i could hang the box in under 20 min on 2.6.22+ w/XFS and raid5 on 7x750GB. i'll try with ext3... Dan's experiences suggest it won't happen with ext3 (or is even more rare), which would explain why this has is overall a rare problem. but it doesn't result in dataloss or permanent system hangups as long as you can become root and raise the size of the stripe cache... so OK i agree with Neil, let's test more... food fight over! :) -dean - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
